The present invention relates to internal combustion engine overhead valve rocker mechanisms.
In certain pushrod type overhead valve engines, such as the Chevrolet® big block, the rocker arms will be attached to the head by a simple stud mechanism screwed into the head. The rocker stud will maintain the rocker in the desired position and allow the rocker to rock about the stud in response to movement from the attached pushrod to actuate the respective valve. However, the rocker stud cannot effectively prevent the rocker from rotating about a longitudinal axis of the rocker stud. Therefore, to prevent such rotation and the resulting misalignment of the rocker with the valve stem, pushrod guides are used in the engine to generally fix the positioning of the pushrods. The pushrods are allowed to move up and down in response to rotation of the camshaft but are prevented from substantial side-to-side movement. This general fixing of the pushrods by the pushrod guides helps prevent rotation of the rockers about the rocker studs.
High performance versions of such engines will often use roller rocker arms. A rocker stand is mounted to the head, usually by bolting the stand to the same threaded bores as the rocker studs use. The rocker stand supports a shaft mounted transversely to the rocker stand mounting bolt and the roller rocker arms are mounted by roller bearings on the shaft. This roller bearing mounting of the rocker arm is more efficient and can better withstand higher actuating forces found in high performance engines than can a standard rocker arm. Since the rocker stands are mounted to the head by the single bolt, they are subject to rotation about the bolt. The shaft is usually fixed to the rocker stand at both ends and so the roller rocker arm will also rotate with the rocker stand about the mounting bolt. Therefore, some provision must be made to prevent rotation of each rocker stand and respective roller rocker.
One approach to preventing rotation of the rocker stands has been to mount several roller rockers on an extended rocker stand. However, such rocker stands are complex, expensive to manufacture and not easily set up. Also, substantial machining of the cylinder head is required to accommodate such stands. See FIG. 7 (Prior Art) which shows a portion of such a known multiple rocker stand which supports four roller rockers, two of which are needed for each big block cylinder head.
Another approach has been to bolt adjacent rocker arms together to prevent rotation. See FIG. 8 (Prior Art) which shows such a known pair of rocker assemblies 110 and 112. Each of the rocker assemblies 110 and 112 include a tab 114 and 116, respectively, which can be bolted together by bolt 118 to prevent rotation of the rocker stands. While this method is effective in preventing rotation of the rocker roller, it is also expensive as it requires different intake and exhaust rocker stands. Further, because of the canting of the rocker stands, if tight tolerances are not maintained, or the rocker stands are shimmed at all, the geometry of the two rocker stands with respect to each other can change enough such that the bolt 118 cannot be passed through one or both of the tabs to allow the rocker stands to be bolted together. This may then require further expensive and time-consuming machining of the rocker stands and/or cylinder head to provide the desired dimensions and tolerances.
In addition, it has been found that many aftermarket cylinder heads are not machined to the proper dimensions. When roller rocker components having correct dimensions are installed on such cylinder heads, the components may not have the correct geometry to operate properly. Although the roller rocker components are correct and it is the cylinder head that is incorrect, the purchaser tends to assume the opposite, leading to poor customer relations that are unjustified for the supplier of the roller rocker components.
Therefore, a simple, cost effective mechanism is needed for mounting rocker roller arms to a cylinder head while preventing rotation of the rocker roller arms about a rocker stand mounting bolt. Such a mechanism should be able to operate properly even when the dimensions of the cylinder head are beyond design tolerances.